The ability of radiation detectors to operate as thermal detectors has allowed them to be used as non-contact alternatives to many conventional temperature sensors. For example, infrared sensing devices are being used in industrial applications to detect temperature differences between neighboring target locations. Such applications might include measuring heat gain or loss from machinery, plumbing or electrical lines. Typically, radiation sensors respond to changes in thermal radiation in the order of less than 1/10 second. This speed allows the sensors to operate in a quickly changing detection environment, further increasing their desirability.
One particular application of radiation detector use is in the quality control environment. The sensors can be used to detect a dynamic pattern of temperatures or temperature changes as found on assembly line and conveyor belt processes. A detector suitable for such a process is described in U.S. Pat. No. 4,831,258 to Paulk et al., and assigned to the assignee of the present invention. This detector is shown in FIG. 1 being used in conjunction with the quality control testing of a hot adhesive application process. A hot adhesive dispenser 12 applies adhesive 16 onto a substrate 9, such as a portion of a box top or other packaging piece. A dual element sensor 10 is mounted beside and downstream of the dispenser 12 and houses thermopiles 74 and 76.
The thermopiles 74. 76 of the sensor 10 are packaged together in a common can 77 with their cold junctions held at a common temperature. Through a lens 82 and aperture 79 in one end of sensor 10, thermopile 74 detects the thermal radiation of the dispensed adhesive target and thermopile 76 detects the thermal radiation of the adjacent reference portion 18 of the substrate 9 which does not have adhesive applied to it. With the two thermopiles coupled electrically in series, the dual element sensor 10 produces a signal of the thermal difference between the detected adhesive and substrate reference area 18. This signal is transmitted to remote display meter 22 by line 24. Meter 22 provides an LED bar graph display 26 of the sensed thermal difference and provides 2 sets of 3 LED displays 29 on opposite adjacent sides of the bar graph display 26. Hence, an indication of sensed heat flux can be seen by the user from three different sides of display meter 22.